Incorporating a telephone interconnect call mode of operation onto a trunked system has generally been constrained by the simplex (voice and data signalling) nature of trunked system subscriber units. Similarly, signalling and call processing by fixed-end control equipment is also simplex formatted. While the introduction of duplex voice/RF-capable subscriber units utilizing simplex data signalling with fixed-end control equipment improves the grade of uses interconnect service, their use restricts the amount of dynamic control and call status changes possible while processing a current, duplex voice-only call.